Transmission control circuit



Oct. 22, 1935. R. B. HEARN TRANSMISSION CONTROL CIRCUIT Filed June 30, 1954 /NVEN TOR R. B. HEA RN Patented Oct. 22, 1935 UNITED STATES PATENT OFFIQE TRANSMISSION CONTROL CIRCUIT Application June `30, 1934, Serial No. 733,153

4 Claims.

The present invention relates to the transmission of currents from one line to another and more particularly to transmission control and repeating arrangements. A

Where currents for signal or control purposes are sent over lines that are divided into sections or that are branched, some form of repeater may be used to route the currents over the proper paths. When the control currents are used at the junction points or elsewhere to set up aparticular circuit condition for the transmission oi other message waves, a difculty may arise from the liability of false operation of the circuit control apparatus by -disturbing currents.

The present invention provides for repeating and utilizing the signal or control currents and makes provision against false operation of the circuit conditioning apparatus by interfering currents.

In a specific form, the invention may be embodied in a system for transmitting speech or visual-image currents over interconnected lines containing repeaters. The control currents in the specific form to be described are direct currents which are transmitted in part over the Isame circuits as carry the speech or image currents and they are used to condition these circuits for one-way transmission at a time, of the speech or message currents. Additional circuit control functions may also be performed as required.

These control currents are repeated from one line to another as conditions may require.

On lines exposed to interference, especially open wire lines, lightning or other currents of high intensity and short duration are liable to interfere with proper control of the transmission circuits by the control currents and it is a general object of the invention to minimize such interfering effects.

Referring to the attached drawing, there is shown in Fig. 2 in schematic form so much of -a complete picture transmitting and talking circuit, With direct current control equipment, as is necessary to a complete understanding of the invention, While Fig. 1 is a simplified diagram to show the essential operation of the control circuits.

A general understanding of the invention in its essentials Will be facilitated by rst considering the simplified circuit diagram of Fig. 1 showing an east line LE and a west line LW associated as the two sides of a four-wire circuit, with direct current control apparatus ras shown. Assuming that the control currents are to be transmitted in the eastward direction over the line LE. the receiving relay Ri shifts its armature from contact l to contact 3, closing circuit from ground at 2 over the control lead Il) and normal contact il to energize the sending relay S2 of the next line section. The sending relay in the manner to be 5 described later on projects control current over the next line section. A delay device D2 energizes with S2 and opens normal contact I2. If the energizing circuit of S2 and D2 is momentarily broken, device D2 will not close contact I 2 because l0 of its delay action feature.

With the circuit closed through as above traced, if a lightning flash or other disturbance occurs on the lines, such as to lcause both polarized relays R1 and Rz to shift their armatures to their oppol5 site contacts for a brief instant of time, the direction of the control current over the lines will not be reversed. For, even though the armature of relay R2 closes Contact i3, it finds the contact i2 open and therefore cannot supply ground to the 20 control lead I0 such as might cause energization of Si. The lead it is shown as branching to the repeater equipment of other lines so that if a ground is placed on the lead by any receiving relay, the sending relays of all the lines through 25 which the conductor I0 is extended are energized.

The control repeater equipment includes circuit control apparatus (not shown in the simplied Fig.

l) for conditioning repeaters in the lines LE and LW for one-way transmission. The circuit pro- 3G visions that have been described for preventing a reversal of the control currents also prevents, in a manner Athat will be described, the conditioning of this repeater equipment for the wrong direction of transmission.

In Fig. 2 four different lines are shown radiating from the central switching or branch point indicated by the rectangle 20. These four lines comprise rst the four-wire subscribers loop including the east line LE and the west line LW 'i0 and the three two-wire inter-office lines L1, L2 and L3. The circuits enclosed in the rectangle 25 are preferably an interconnecting network of the type described and claimed in an application for Letters Patent of C. W. Green, Serial No. '730,- i5 493, flied June 13, 1934. That is, each of the lines radiating from this branching point is interconnected with each of the other lines so that transmission received over one line is sent out over each of the other lines. For this purpose, 50 as disclosed more fully in the Green application, each of the lines as it enters the network 20 is in the form of a four-wire circuit comprising `a transmitting branch and a receiving branch.

Y ing through the ampliiier I4 toward the network 2i3 and the other leading through the amplifier i5 from the network 20 toward the line L1. In similar manner line L2 terminates in a pair of one-Way branches containing repeaters I4' and I5 and. line L3 is similarly provided with oneway branches including amplifiers I4 and I5", the hybrid coil arrangements for these latter lines not being shown. All of the lines could be fourwire lines like LE, LW or two-wire lines like L1, SEC.

The dotted lines and arrows inside the rectangle 2s show the paths taken by the message waves transmitted and received over the various one-way circuits radiating Vfrom the network 2li. For example, waves received over the line LE through the amplifier divide between the three the same line or the o-pposite -side of the same' four-wire line by the nature of the interconnecting network as shown more fully in theGreen application.

The four-wire line 'LE-LW leads out to a station I which may contain any suitable trans- Y mitting and receiving apparatus, but will be assumed for purposes of disclosure to include picture transmitting and talking apparatus which may be of the type shown for example in application for Letters Patent by A. Weaver Serial NoA 734,152, filed July 7, 1934. Of this apparatus only the sending relay 9 and the receiving relay 8 are shown in the drawing. Speech currents or currents representing a picture are sent'out from the station 'l over the line LE and currents of similar character are received at the station over the line LW. `The receiving relay 8 may be arranged as in the Weaver application or otherwise to actuate a signal notifying an attendant 'that a picture is about to be received. The sending relay 9 may be operated manually or otherwise associated with thev picture transmitting machine so that this relay is actuated when pictures are to be sent out over the line LE. The circuit details of this terminal apparatus are more fully disclosed in the *Weaver application referred to. Y

It will be understood that a similar station is present on each subscribersloopl entering offices to which the lines L1, L2, and L3 extend so that when a-picture is sent out or speech Vis trans-V j dicated invFig. 1 above described. The repeater associated with the line LE-LW comprises polarized receiving relay Ri and sending relay S1, an

Vauxiliary sending relay '22, a slowrelease relay 23made slow because of the connectionrof the combination resistance and capacity 24 in the energizing circuit of this relay, and a'local or switching relay 25.

The'control current repeater associated with the line L1 is generally indicated at 2| and differs from that associated with the line LE-LW only4 in the difference in type of control current sent out on the line. The repeaters for the lines L: and L3 may be identical with that for line ALi and are similarly numbered as 2l, ZI. Each of these repeaters is associated Vwith its corresponding line through suitable composite arrangements l CXI, CX-2 or CX-3 which may be ofi any suitable type known in the art for enabling direct current to be sent over the corresponding line without interfering with Ythe transmission of speech or picture currents. Y

The operation of Fig. 2 will now be described. Let it be assumed that a picture is to beV sent from'the station I on theline LE`LW .to corresponding stations on other subscriber lines. The attendant at the station i prepares the transmitting machine to transmit the picture and connects it to the terminals of the outgoing line LE, at the same time closing'a suitable energizing circuit for the sending Vrelay e causing this relay to attract its armature, breaking at its back contact the energizing circuit for the receiving relay ground'over the simplex circuit comprising the two sides 'of the line circuit LE betweenthe repeating coils I6 and Iii',V normal contacts of the sending relay S1 of the repeater circuit, and wind- 8 and closing at its front contact a circuit from i5 ing of receiving relay R1 to battery, Vcausing the 0 latter relay to become energized. The circuit just traced remains closed for the duration or theV transmission of the picture.

The receiving relay R1 when energized closes a circuit from ground at the armature of relay 2i?, 35

normal contact 2, iront contact 3, normal contact I9, to the control lead I0 which leads to allV of the other repeaters. The eiect at the various other repeaters can be seen from considering the effect o-f this ground on the lead I0 at the repeater 2|V associated with the line L1. This ground on conductor I0 causes the energization of the sending relay Si and auxiliary relay 32, the circuit extending from conductor i0 through n'ormal contact 3S, normal contact II and the windings of relays 32 and Si to battery. Relay S1 in shifting its armature reverses the current on the line Li, the effect oi.' which is described later on. Relay 32 when energizing closes a circuit through the/winding Vof relay 33 which en- 50 put side of the repeater I4 thus disabling this side 55 of the four-wire circuit terminating the linefL1. At the upper armature and back contact of relay 35, the normal ground extending to the contact I3 of the relay R11' is broken. The lighting of the lamp 36 indicates to an attendant that transmission is taking place throughthis station in a direction from the network 2li toward the lineLi.

A similar action takes place -in'each of the other repeaters 2I associated with'the line L2 and La 55 since the lead I0 is connected in a similar manner to those repeaters. The corresponding ampliner elements I4' and I4" are disabled by the closureroffa short circuit by relays similar to 35.

Transmission can now take place from the station 'I over the line LE to the branching network 20 and thence over each of the lines L1, Laand La.` The eiect of reversing the current in this manner on line L1 can be seen from consic'leringE the repeater 2| to be receiving from the similar repeater at the distant oiiice to which line L1 leads. Suppose that the sending relay at such distant station had operated in response to control current received from a subscribers line or another inter-cnice trunk. Such current reversal would energize relay R1' and ground would have been placed on the conductor l through the front contact I3 of relay R1 and the contact l2 of the relay 35. This ground would have had the effect oi energizing all of the auxiliary and sending relays associated with each of the other lines including auxiliary relay 22 and sending relay Si in the repeater associated with the line LE-LW. This Would cause the relays 22, Si, 23 and 25 of that repeater to energize, sending current out over the loop comprising lines LE and LW and the Winding of relay 8 and, at the central station, lighting lamp 26, closing a short circuit across the input of repeater 4 and breaking the connection at point 2. Thus the picture apparatus at the substation on line LE-LW Would have been conditioned for receiving.

As was explained with the aid of the simplified diagram of Fig. l, if a sudden disturbance occurs on the lines after the direct current repeaters have been operated to condition the circuit for transmission in one direction, the momentary operation of the receiving relays causing their armatures to shift to their opposite contacts or to vibrate, will not have the effect of changing the conditioning of the line for the message transmis sion.

For example assuming as at first that transmission is taking place from the station l on the line LE-LW to the other lines, relays 32 and Si (as Well as the corresponding relays in the repearters associated with lines L2 and La) Will be operated and the relays 33 and 35 Will likewise be operated. If now a disturbance on the lines momentarily causes relays Ri and R1' to shift their armatures to their opposite contacts, this will not have the effect of releasing relay 35 nor energizing relays Si and 22 becauseof the slow release characteristics of relay 33. Thus, the shunt across the input of repeater lli from the armature and front contact of relay 35 remains unbroken and the lamp 36 remains illuminated.

A prolonged opening of the circuit of lead i3 will restore the apparatus to normal. For example, after the picture has been transmitted from the station 'l on line LE-LW, and the relay 9 has been released for a suilicient length of time, receiving relays R1, 3l and Si will fall back and after a sufcient time the slow relay 33 will fall back. The time required for the latter relay to be deenergized is determined by the constants of the circuit particularly the resistance and condenser combination 3d. For example., when the relay 32 releases and removes ground from its front contact, current continues to flow from the battery associated With relay 33 through the winding of that relay, through resistance and into the condenser to ground. The condenser slowly charges up and reduces the current ilow to the point Where relay 33 releases after which relay 35 falls back and restores the circuit to the condition shown in the drawing. This same action occurs at each oi' the other repeaters 2l associated with the other line such as L2 and La.

The receiving relay corresponding to the relay of the substation 'l is restored when the relay Si releases since positive battery of say 135 volts potential is now applied to each side of the line LE-LW, one battery being connected through the back contact of the relay Si arid the Winding of relay R1 and the other battery being connected to repeating coil il.

It is to be understood that the invention is not limited to the particular' circuit details disclosed herein, but is capable of Wide modification and variation within the scope of the app ended claims.

What is claimed is: y

1. In combination, lines each having a sending circuit and a receiving circuit, a receive relay for y each line each having its Winding operatively connected to the receiving circuit, a send relay for each line having an energizing circuit, and a time delay device for each line controlled from the energizing circuit for the send relay of the respective line, the receive relay and the time delay device of the same line conjointly controlling the send relay energizing circuit of another line.

2. In combination, in a control current circuit for transmission lines, a first repeater, a second repeater associated with respective lines, each repeater comprising a send relay and a receive relay, the receive relay of the first repeater controlling the send relay energizing circuit o! the second repeater, and means for preventing transient impulses from causing energization of the send relay of the first repeater during the intended period of operation of the send relay of the second repeater comprising a sluggish device operated under control of the send relay energizing circuit of the second repeater', said device controlling the send relay energizing circuit of the first repeater.

3. In a signalling system, a line divided into sections, a repeater for each line section, each repeater comprising a receiving relay and a sending relay, the energizing circuit of the sending relay being controlled by a contact on the receiving relay of the same repeater, a slow release relay in each repeater controlled by the energizing circuit of the. sending relay, the sending relay energizing circuit of one repeater being controlled jointly by contacts on the receiving relay and slow release relay of another repeater.

4. In a system for the transmission of pictures over line Wires, a direct current control circuit extending over the line for conditioning the line for transmission in only one direction at a time comprising relays controlled by the direct currents on the line, and means preventing false operation of said conditioning circuit by short disturbing impulses on the line comprising a delay device interposed in the control circuits of the conditioning relays to prevent their release in response to short impulses.

RICHARD B. HEARN. 

